1. Technical Field
This disclosure relates to a droplet discharging head used for a printer, facsimile machine, projector, and the like, a liquid cartridge provided with such a droplet discharging head, and a droplet discharging device on which such a liquid cartridge is installed.
2. Description of the Related Art
Conventionally, a lot of techniques have been researched and known regarding droplet discharging heads, such as droplet discharging heads for discharging liquid resist in a droplet form, droplet discharging heads for discharging a DNA specimen in a droplet form, droplet discharging heads for discharging ink in a droplet form, and the like (refer to Patent Documents 1 to 9, for example).
On an ink-jet (droplet discharging) recording device used as an image recording apparatus (image formation apparatus) such as a printer, facsimile machine, plotter, and the like, there are installed an ink-jet head as a droplet discharging head including a nozzle for discharging an ink droplet, an individual liquid chamber (also referred to as an ink flow path, discharging chamber, liquid pressure chamber, and flow path) communicating with the nozzle, and a driving unit (pressure generating unit) pressurizing ink in the individual liquid chamber. In the following, the ink-jet (droplet discharging) head is mainly described.
Examples of technique for such an ink-jet head include driving units using a piezo-electric element (Patent Document 1), electrostatic force (Patent Document 2), bubble pressure (hereafter referred to as a bubble method) (Patent Document 3), and the like.
Among the above-mentioned techniques, the ink-jet head based on the bubble method includes wiring to which a signal is applied, a heater capable of generating heat via the wiring and of heating ink so as to generate bubbles, and an individual liquid chamber filled with the ink. The ink-jet head discharges the ink from the individual liquid chamber in accordance with bubble generating energy from the heater.
In general, an ink-jet head in which a nozzle axis direction and a flow direction of ink supply are arranged in parallel is referred to as an edge-shooter type and an ink-jet head in which the nozzle axis direction and the flow direction of ink supply are arranged orthogonally to each other is referred to as a side-shooter type.
The edge-shooter type is characterized in that a basic structure is obtained by disposing the heater and the wiring on a flow path plate and attaching a top plate. Thus, the edge-shooter type is suitable for mass production, increase in nozzles, and downsizing.
By contrast, the edge-shooter type has demerits in that a speed of response to refill is slow, discharge power is smaller than that of the side-shooter type, and cavitation is likely to be generated. In accordance with there characteristics, the edge-shooter type had been widely used in the early stages of printers and has been partially employed in line head printers and the like.
On the other hand, in the side-shooter type, a nozzle outlet is positioned directly above the heater, so that an amount of ink is determined by a measure and an amount of discharged ink becomes constant. Further, air bubbles are communicated with the air, so that no cavitation is generated.
In accordance with this, life of the head is improved. Further, a direction where the air bubbles are generated corresponds to a discharge direction, so that the discharge power is enhanced. In addition, a large shock wave is not transmitted to a flow path side, so that the speed of ink refill is fast, and meniscus becomes stable, so that the side-shooter type is suitable for high-speed printing. Currently, the side-shooter type has been mainly employed for printers based on the bubble method.
When using a driving unit based on any of the bubble method, piezo-electric method, electrostatic force method, or the like, there have been increasing demands for ink-jet printers to perform printing of higher image quality, faster speed, and higher reliability in recent years. However, there have been many problems to overcome so as to satisfy these demands.
One of such problems is air bubbles. Some air bubbles remain in an ink supply system upon initial filling of ink and other air bubbles enter upon replacing an ink cartridge. There air bubbles are not particularly problematic as long as they are in a common liquid chamber but pose a problem when these air bubbles are conveyed to the individual liquid chamber via the common liquid chamber.
In other words, air bubbles conveyed to the individual liquid chamber and entered a heater portion absorb pressure for discharging the ink regardless of any of the above-mentioned driving units. This may become a cause of failure of ink discharge. In view of this, various measures have been proposed so as to remove the air bubbles. For example, as a proposal regarding the common liquid chamber, Patent Document 4 discloses an air bubble trap disposed on a top plate of the common liquid chamber so as to prevent the air bubbles from entering the individual liquid chamber.
Patents Documents 5 and 6 disclose a hole for ejecting air bubbles disposed on the common liquid chamber. Patent Document 7 discloses concavity and convexity disposed on a wall surface of the common liquid chamber as the air bubble trap.
Patent Document 8 discloses a flow path dedicated to ejection of air bubbles in which ink and air bubbles experience suction from the flow path by a suction recovery mechanism upon recovery operation of the ink through suction, for example. However, in this case, a structure of a peripheral portion of a printer head becomes complicated, so that cost would be increased.
Patent Document 9 discloses ejection of air bubbles in which air bubbles which have entered the individual liquid chamber are collected using air bubbles generated in a second heater and the air bubbles are ejected by an air bubble ejecting mechanism. However, the structure becomes complicated and cost would also be increased in the same manner as in the above disclosure.
Patent Document 10 discloses a technique in which the air bubble trap is disposed on an opposite side of a heater substrate, a communication hole is formed to the common liquid chamber from the air bubble trap, and air bubbles are conveyed to the communication hole.
Patent Document 1: Japanese Laid-Open Patent Application No. 2-51734
Patent Document 2: Japanese Laid-Open Patent Application No. 5-50601
Patent Document 3: Japanese Laid-Open Patent Application No. 61-59911
Patent Document 4: Japanese Laid-Open Patent Application No. 2002-103645
Patent Document 5: Japanese Laid-Open Patent Application No. 10-166587
Patent Document 6: Japanese Laid-Open Patent Application No. 2003-72065
Patent Document 7: Japanese Laid-Open Patent Application No. 10-315459
Patent Document 8: Japanese Laid-Open Patent Application No. 9-207354
Patent Document 9: Japanese Laid-Open Patent Application No. 7-195711
Patent Document 10: Japanese Laid-Open Patent Application No. 10-024572
However, in these disclosed techniques, although it is possible to remove those air bubbles passing by the vicinity of the air bubble trap to some extent, it is difficult to remove those air bubbles entering the common liquid chamber distant from the air bubble trap and the air bubble ejecting mechanism, namely, air bubbles passing through a central portion of the common liquid chamber. These air bubbles eventually enter the individual liquid chamber and become a cause of failure of discharge.
In this manner, various measures to deal with air bubbles in various techniques which has been disclosed (Patent Documents 1 to 10) have both merits and demerits, so that none of them completely provides an intended effect.